The present invention generally relates to control valves in high pressure fluid transfer systems, such as waterworks systems. More particularly, the present invention relates to an anti-cavitation seat for use in control valves so as to impart anti-cavitation and low-noise properties.
Main valves, such as that illustrated in FIG. 1, are regularly used in high pressure fluid transfer systems, such as waterworks systems. Such main valves, generally referred to by the reference number 10, are also referred to as basic valves, flow control valves, and pressure reducing valves and the like. These valves include a body 12 defining a fluid inlet 14 and a fluid outlet 16, generally on opposite ends of the body 12. The inlet 14 and outlet 16 are operably connected to piping or the like so as to deliver the fluid in a controlled manner. A seat 18 is disposed between the fluid inlet 14 and outlet 16, and in conjunction with a stem assembly controls the water flow through the valve 10. In order to open and close the valve 10, and control the flow of water therethrough, a cover 20 is secured to the body 12 and with a diaphragm 22 defines a pressure chamber 24. Fluid is moved into and out of the pressure chamber 24, causing the diaphragm 22 to flex outwardly towards the seat 18 and inwardly into the pressure chamber 24.
A stem assembly includes a stem 26 which extends through a diaphragm washer 28, on one side of the diaphragm 22 and a disc retainer 30 having a disc 32, which engages an upper lip of the seat 18 in order to close the valve 10. When the pressure in the pressure chamber 24 proportionally less than the pressure at the valve inlet 14, the pressure forces overcome spring 38 forces which biases the diaphragm washer 28, diaphragm 22, disc retainer 30 and disc 32 upwardly into the pressure chamber 24, thus opening the valve 10. However, when the fluid pressure within the pressure chamber 24 is equal to or greater than the valve inlet 14 pressure and valve outlet 16 pressure, as illustrated in FIG. 1, the fluid pressure assists the force of the spring 34 and moves the diaphragm 22, and thus the associated diaphragm washer 28, disc retainer 30, and disc 32 towards the seat 18, until the disc 32 engages the upper lip of the seat 18, as illustrated, in order the close the valve 10. Thus, the diaphragm 22, stem 26, diaphragm washer 28, disc retainer 30 and disc 32 slidably move with each other relative to the seat 18 in order to open and close the valve. The interplay between the fluid within the valve 10, the strength of the spring 34, and the pressure applied to the pressure chamber 24 dictate the degree which the valve 10 is opened or closed, and thus the amount of fluid which is allowed to pass through the valve 10 downstream.
When subjected to high-pressure differentials or high flow rates, valves often exhibit excessive noise and vibration. This is usually attributable to the phenomenon of cavitation, which can range from relatively harmless levels called incipient cavitation to significantly more acute levels that actually damage valves and related piping. This can be loud enough to cause hearing loss in plant personnel if subjected to it for extended periods of time.
Cavitation occurs if the velocity of the fluid in the valve seating area becomes excessive, creating a sudden severe reduction in pressure that transforms the liquid into a vapor state, resulting in the formation of literally thousands of minute bubbles. The subsequent decrease of velocity and pressure rise that occurs after the valve seating area, when the pressure rise condition resumes, causes these vapor bubbles to collapse at the rate of many times per second. Should this occur in close proximity to any metal surface, damage can take place. Over time, this can lead to valve failure due to the vibration and/or erosion. Minimizing or eliminating these conditions that adversely affect operation and service life of the valve continues to be one of the most serious challenges encountered in the daily operation of a water distribution system, such as municipal water systems and the like.
To overcome the adverse effects of the orifice action of the valve, it has become common practice to design the valve so as to break up the flow through the valve into a multitude of small streams which are then led through convoluted paths to produce energy losses in the fluid. Such designs are known as torturous fluid flow redirection. Valve assemblies are known, such as those produced by Ross Valve Manufacturing Company Inc., which utilize aligned plates that serve to suppress vibration, pressure fluctuations, cavitation and noise. For example, an upstream corrugated plate may be selectively slid into place to control the flow. A downstream plate having a plurality of apertures creates a plurality of jets which reduces the pressure flow through the set of plates. However, the number and size of aperture in the plates, the number of plates, and their spacing are determined by fluid flow, and varying flows can make such orifice plates ineffective.
Yet other valve assemblies are known in which interfacing canisters having apertures form a tortuous fluid path are also known. For example, Singer Valve Inc. offers an anti-cavitation trim having interconnecting canisters with a plurality of small round apertures which overcomes many of the previous problems of the “stacked plates” designs. In such two-canister designs as the Singer assembly, one of the canisters serves as a seat while the other canister replaces various components of the stem assembly, and is moved upwardly and downwardly by the stem in relation to the bottom canister so as to open and close the main valve and form a tortuous fluid path between the apertures of the two canisters. The Singer valve is able to effectively and substantially eliminate noise and cavitation. However, this valve assembly is prone to fouling or clogging due to the use of the small round apertures in the canisters. In fact, the fluid must often be filtered before passing through the Singer valve assembly. Moreover, the fluid exiting the canisters of the Singer valve assembly is directed at the housing wall, causing erosion.
While effectively reducing noise and cavitation, these devices are not optimal. The primary disadvantage of such designs is that the valve capacity is significantly lowered, rendering these valves inapplicable in certain situations. Such valve designs also require fairly complex and expensive manufacturing and assembly.
Another problem experienced with the known anti-cavitation valve assemblies disposed within the seat area of the main or basic valve is that they do not allow the use of the same stem assembly components of an existing valve assembly. Thus, the standard valve seat, disc guide, stem, disc retainer, diaphragm, diaphragm washer, etc. must be replaced with the new assembly when retrofitting an existing main or basic valve. It would be advantageous and beneficial to customers wanting to add an anti-cavitation feature to an existing main or basic valve. It would be particularly advantageous and beneficial if the customer could use their existing stem assembly and simply swap out the standard seat with an anti-cavitation seat.
Accordingly, there is a continuing need for an anti-cavitation valve assembly which uses the same stem assembly components of the existing valve, and which can be used in retrofitting existing valves. The present invention fulfills these needs, and provides other related advantages.